Normal map from retopo is having artifacts, despite subsurf
This is due to a poor UV unwrapping (I guess you Smart UV unwrapped your mesh right?), UV maps seams should be hidden as much as possible. Search for UV unwrap 3D head on google to get an idea on where to cut.

Also read the Tangent Basis parts of this post to understand why your normal map create this kind of artifacts: http://wiki.polycount.com/wiki/Texture_Baking